1922] ROBBINS—ROOT TIPS 75 
The secondary root production in the autolized yeast culture was 
somewhat greater and dry matter somewhat less in this case. 
If we compare the growth of roots which had their tips severed 
and were transferred twice to fresh solutions during a six weeks’ 
period with those which grew continuously undisturbed in the 
solution, we find (table VI) that in Pfeffer’s solution plus 2 per cent 
glucose the total increase in length and production of secondary roots 
when the tips were severed and transferred was less than when they 
were left undisturbed; the dry matter was greater. When yeast 
was present the length and secondary root production were not 
affected by the transfers; the dry weight was greater. 
The original P, of the Pfeffer’s solution plus 2 per cent Sede 
was 4.5. The roots which grew for six weeks without transfer 
changed the reaction to P,, 6.3. The original reaction of the Pfeffer’s 
solution plus 2 per cent glucose and 400 ppm of yeast was Py, 5.2. 
The roots which grew for six weeks without transfer changed the 
reaction to a P, of 6.24. 
a a a pit 
Experiment 14—The FPtHR4 oH 
methods and general condi- am 4 t ! 
tions were the same in this ex- : Pe ttt 
periment as in experiment 12. AH ete 
In this case, however, concen- = = seecace 
trations of yeast of 10, 40,and FR scan a ‘ 
80 ppm were used. The root Eyogqpoct it 
tips were grown for the first Ag HHtEE cH 
period with no addition to the zon 
nutrient solution, the yeast amen wanes 
being added in the second we 
period. Unfortunately one of Weote 
the flasks containing the con- - antl 
centrated yeast extract was Fic. 8.—Growth in length of excised corn 
. . . root tips in dark for three periods of trans- 
contaminated with bacteria, fers; solutions used were Pfeffer’s solution 
and most of the cultures were plus 2 per cent glucose, and same solution 
lost in the second period due plus 10, 40, or 80 ppm of autolized yeast. 
to the contamination, leaving but two root tips in each of the con- 
centrations, 40 ppm and 80 ppm. From the data in table VII 
and the graphic representations in fig. 8 it can be noted that the 
